a) Field of the Invention
The present invention relates to a socket prepared from a specific polyimide and used for an integrated circuit (hereinafter abbreviated as IC), and particularly relates to the IC socket for use in a burn-in test.
b) Description of the Prior Art
An IC is generally subjected to a performance test at elevated temperatures, i.e., so-called burn-in test, prior to mounting the IC on equipment in order to confirm its reliability in performance.
In the burn-in test, the electric current is passed through the IC under almost operating conditions by maintaining elevated temperatures of usually 70.degree. to 170.degree. C. and deterioration in the operating state or the presence of an unstable state are checked. The IC accepted by the test guarantees sufficient reliability in various equipment.
An IC socket which is a connection member used to fix an IC on a printed board is exposed to the above elevated temperatures in the state of holding the IC therein. Consequently, thermal resistance is of course required for the insulation materials used for the socket.
However, the burn-in performance test of the IC has recently been carried out at further elevated temperatures in order to accelerate evaluation and improve reliability. As a result, IC sockets made by conventional resins cannot withstand such high temperatures at all in some cases.
For example, glass fiber reinforced resins such as polyethylene terephthalate resin, polybutylene terephthalate resin, and nylon resin can be used up to temperatures of approximately 120.degree. C. At higher temperatures, however, these resins lead to remarkable deterioration of characteristics such as dimensional stability and creep property, and cannot be applied to practical use. Hence, resins having better thermal resistance such as polyphenylene sulfide resin, polysulfone resin, and polyether sulfone resin have been used. Any of these resins, however, practically has a maximum use temperature of 170.degree. C.
In addition to thermal resistance, excellent characteristics are required in many cases for resistance to cleaning chemicals such as isopropyl alcohol, ethyl alcohol, toluene, benzene, trichloroethylene, 1,1,1-trichloroethane, fluorinated methane (e.g. FREON: Trade Mark of a product of E.I. du Pont), acetone, and methanol; steam resistance; and flame retardance. It has hence been difficult to meet these characteristics using conventional resins.
Further, polyimide has been well known as a resin having excellent characteristics such as thermal resistance and chemical resistance. However, conventional polyimide does not melt flow as the polyimide and thus it has been impossible to produce molded articles by common processing methods, for example, injection molding. Although included in the technology of polyimide, a polyetherimide (e.g. ULTEM 1000: TM of a product of General Electric Co.) prepared from tetracarboxyalic acid dianhydride containing an ether linkage in the molecule exceptionally exhibits melt flow at high temperatures. Molded articles can hence been prepared from the polyetherimide by compression molding or injection molding.
However, even though the molded polyetherimide is used as the IC socket, thermal resistance and chemical resistance have still been unsatisfactory.